Threatened with beheading and harried by pirates who robbed them, people fleeing the Niger Delta's Bonny Island this weekend struggled to reach Port Harcourt, the regional capital, as the conflict worsened between armed groups and Nigeria's armed forces.

Barely reported amid attacks on oil facilities and their expatriate staff, the story of what has been happening on Bonny Island - site of the giant Nigeria liquefied gas plant - is a story of two communities in conflict: the better educated and paid incomers from outside the delta and the economically marginalised indigenous Ijaw.

According to reports from Bonny Island and Port Harcourt the problems began two weeks ago with notices placed on the walls of buildings giving those of non-Bonny origins - bankers, shopkeepers and those working at the gas plant - until last Tuesday to leave the island or 'face the consequences'. They spoke of an island overrun with groups of threatening armed men - many with more weapons than the police.

The banks closed down and many of the non-Bonny fled, describing a harrowing flight across open sea or through creeks, pursued by armed men in motorboats who robbed them. Those who chose to remain have been confronted by an influx of Nigerian troops who have flooded the streets, reportedly harassing anyone suspected of being a militant.

Describing the situation on Bonny Island, Ogbonah Nwuke, a local government official, defended the presence of the troops and called on residents to identify gunmen on the island. 'We are insisting that strangers are safe in our midst. The armed forces are not there to threaten law-abiding citizens. We have said in the past that we expected all those who were part of the law-breaking machines to get out of the way. We had pleaded with the people and we got no response. Now we have entered a new phase. We have entered the phase of peace enforcement and that is what is going on in Bonny. '

The escalating crisis in the Niger Delta came as more expatriate workers were pulled out of the oil- and gas-rich region last week amid a spate of violent attacks on both foreign and non-local Nigerian workers. Last Thursday, a key crude oil supply pipeline operated by Agip, the Nigerian subsidiary of Italian group Eni, was blown up.

Following the decision by both Michelin and oil servicing multinational Willbros to quit the delta, Julius Berger - Nigeria's biggest construction firm and a subsidiary of German construction giant Bilfinger Berger - announced it was closing its operations in the region.

The move comes after two of its German staff were kidnapped when their armoured car was blown off the road. 'The current security environment makes it impossible for us to continue our operations in the Niger Delta and to protect our employees,' said a company spokesman.

The decision by Berger also follows a threat from Nigeria's largest oil workers' union, Nupeng, to pull all its members out of the delta if there was no improvement in the security situation.

With the continuing high price of oil, Nigeria's inability to guarantee the security of its oil production has been catapulted up the international agenda. The massive theft and smuggling of so-called 'blood oil' from the world's eighth biggest oil producer has ramped up the pressure. Nigeria's President, Umaru Yar'Adua, has said a return to security could see output rise by 1.2 million barrels a day.

Details of the latest incidents emerged as British Prime Minister Gordon Brown announced he would be offering military training and assistance to the government to help bring back security to the delta, which has seen its oil output decline by almost a quarter in the past two years because of the spiralling violence.

That offer was greeted with scepticism by both human rights organisations and experts on the situation in the delta, who point out that senior members of Yar'Adua's People's Democratic Party have been responsible for fomenting a large part of the violence - even arming the Ijaw militant groups fighting the government for an equitable share of the oil wealth of their region. Although British officials insist no deal has yet been done over military assistance, others have been attracted to the potential money to be made out of the crisis - private military corporations allegedly including the US firm Blackwater and the British firm Aegis.

Despite often being portrayed as a straightforward conflict between indigenous groups and the oil multinationals following decades of environmental damage and neglect of the local population in the delta, the reality of the situation into which the British government has offered to intervene is far more complex.

A recent report by Human Rights Watch portrayed a murky world where the boundaries of delta politics and the activities of the delta 'youth' groups from the creeks - both criminal, armed community groups and also those in the pay of powerful government politicians - are often overlapping if not indistinguishable.

While groups such as Asari Dokobo's Niger Delta People's Volunteer Force and the Movement for the Emancipation of the Niger Delta have portrayed themselves as being at the forefront of the struggle against the government and the economic marginalisation of the delta, members of the same groups - according to evidence collected by Human Rights Watch and others - have also acted as paid thugs for pro-government politicians, and as members of 'cults' or violent criminal gangs.

The staple activities of the gangs are robbery, kidnapping, piracy and - most lucratively - the so-called practice of 'bunkering' or stealing oil from pipelines which have allowed the 'cults' to amass huge amounts of money, influence and arms to the degree that they often outgun the police.

Since the largely rigged 2007 elections that brought Yar'Adua to power, the Niger Delta has seen a sharp rise in cult-related violence with rival gangs the Icelanders led by Ateke Tom and the Outlaws of Soboma George fighting for political patronage and apparently immune to prosecution through protection by members of Yar'Adua's party.

A further element in this already volatile mix is the presence of the largest insurgent group - Mend - which has claimed responsibility for numerous attacks on the delta's oil and infrastructure as part of its campaign for local people to have a share of the energy wealth being generated. Its alleged leader, Henry Okah, was arrested in Angola and extradited to Nigeria where he is facing a trial in secret on allegations of treason, terrorism and gun-running.

Amnesty International is one of the organisations that is dubious whether a military solution alone - aided by British military advisers and training - will have any impact on the situation in the delta.

Audrey Gaughran of Amnesty, who recently returned from a visit to the delta, said: 'While clearly there is a real security crisis in the delta it can't be tackled by looking at the security alone. It requires a comprehensive answer and there does not seem to be a commitment to a comprehensive solution. The president says that he has a plan but it is hard to see what grip he has on the situation. When we visited the delta we were concerned - where is the government? It felt invisible.'